For drinking water purification, removal of chlorine, VOC's, and heavy metals such as lead, is considered essential. Typically packed beds of carbon are used for removal of chlorine and VOC's but activated carbon cannot remove heavy metals very efficiently. For the heavy metal removal, ion exchange resin beads are generally used in the packed beds with activated carbon. These resins are expensive and take up space. Thus the beds have to be made larger than is practical.
Use of inorganic materials that contain acidic groups such as amorphous titanium silicate or tin silicate to remove heavy metals is known. Titanium silicates or tin silicates within the composition range of mole ratio of silicon to titanium or tin from 1:4 to 1.9:1 are known to be especially useful for heavy metal removal. Such materials are available in the form of fine powders. These powders can be mechanically mixed with carbon and used in packed beds to obtain desired heavy metal removal. A packed bed can contain a mixture of carbon and ion exchange resin or carbon and titanium silicate, etc. When two different substances with different functions are used in packed beds, the size of the bed has to be made large enough so that sufficient contact efficiency with the fluid is obtained. The contact efficiency becomes a very important issue in the case of liquids such as water because of high diffusion resistance encountered in the liquid phase. In addition, the packed beds offer much higher resistance to flow, reducing the flow rate for a given pressure drop. Packed beds also offer poor particle filtration efficiencies and inconsistent performance due to channeling, etc. Another problem with this approach is that the fine titanium silicate powder gets washed out with the effluent which is not desirable. The fine powder increases resistance to flow causing low processing rates.
A compact system to remove heavy metals as well as VOC's and chlorine with high geometric surface area to obtain high flow rates and good particle removal efficiencies, is thus desired.
The present invention fills this need.